Transisters

If you are an electronic enthusiast, you may not want to read this article through, because transistor is like the A in electronics alphabet. Yet, if you read this article you will see transistors in a different way. Back in my university days I was able to understand it in my own unique way. This way I remembered all the important things about transistors and that came back handy in my exams. Even though we learned lots of theories about basic electronic components, if we fail to use them in real life applications this effort will be like a treasure berried in your backyard and you decide never to dig your backyard for the rest of your life. In modern days you can make electronic circuit without the knowledge of electronic basics. Sensor models, programmable circuits have conquered each student’s projects and assignments. I believe those modular electronics units should be moved to primary school syllabus and should focus on basics in higher education. If that was the case, I would have understood electronics better and would have done so many projects by now.

Transistor is a semiconductor device. Semiconductor is a special material which conducts electricity in certain conditions. That means it can act as a conductor as well as a non-conductor (insulator). Most commonly used semiconductors are Silicon and Germanium. If we take silicon considering the conductivity of electricity and heat, it can act as metals like gold and copper or insulators like glass and PVC.

It is better to refer the atomic structure of semiconductors if you want to learn more about semiconductors. For this article let’s just say you cook semiconductors with other ingredients to use them in special application.

 

Figure 1: Silicon Atom last energy level

 

If you study the atomic structure of silicone you should know that there are 4 electrons in its valence band. Atoms tend to be neutral in their normal state, meaning for silicon to be neutral it must have 8 electrons in its last energy level. Therefore, silicon atom in pure silicon lattice has another four atoms surrounding it. This way atom will be neutralized by sharing and electron with each 5 silicon atoms. The neutral state of Silicon has no use for us. There are two states that changed the world namely p-type and n-type semiconductors. Figure 2 is the atomic structure of silicon lattice. Orange and black dots are electrons. Black electrons are electrons from atoms not
illustrated

Figure 2: silicon lattice

If you add some impurities which lacks an electron in its last energy level (Boron) then material has positive charge and it makes the material electrically conductive. This is p-type semiconductors. Now you know what a n-type semiconductor is too. Impurities with 5 electrons (Phosphorus, arsenic, bismuth…) in its last energy level are added with silicon atoms. This makes the material negatively charged. These are called n-type semiconductors and they are also electrically conductive.

Figure 3: P-type lattice

Figure 3 illustrates a p-type semiconductor. The empty slot created by the lack of electron is called holes. The neighboring electron will be attracted to this position creating a new hole and that hole can attract another one. If we apply voltage across this lattice there will be a current flow due to this effect.

 

Figure 4: N-type Lattice

 

Figure 4 illustrates an n-type semiconductor. Prosperous has 5 electrons in its last energy level. Therefore, this semiconductor has a negative charge. When we apply a voltage current will flow due to that free electron.

Thusithanjana Thilakarathna

(Published on Happinez Magazine)